Proposals have been made to place taxiing motors in the wheels of the main landing gear of an aircraft in order to enable the aircraft to be maneuvered and taxied on the ground without requiring thrust from its engines. For this purpose, the motors are powered by means of an electricity generator driven by the auxiliary power unit of the aircraft.
Main landing gear wheels are generally heavily loaded and they have the potential of developing a high level of driving force. Nevertheless, main landing gear wheels are generally fitted with brakes, and as result there remains very little space available for receiving a motor of significant power. Various arrangements have been proposed for mitigating such lack of space.
For example, document US 2006/055779 proposes placing the taxiing motors in the nosegear wheels, which generally do not include brakes. A large volume is thus available for receiving motors of significant power. Furthermore, the generally smaller, rolling radius of the tires of nosegear wheels makes it easier to develop a driving force of greater magnitude for equivalent torque. Nevertheless, the nose landing gear is much more lightly loaded than is the main landing gear. Commonly it supports 10% to 15% of the weight of the aircraft, which percentage may drop to as little as 5% in certain tail-heavy situations. The driving force that can be developed by the nosegear wheels may then be insufficient for moving the aircraft, particularly if the taxiway is sloping, wet, or even icy.